U.S. patent number 5,197,805 [Application Number 07/767,983] was granted by the patent office on 1993-03-30 for temperature sensor protection tube.
This patent grant is currently assigned to Pyromation, Inc.. Invention is credited to Richard F. Wilson.
United States Patent |
5,197,805 |
Wilson |
March 30, 1993 |
Temperature sensor protection tube
Abstract
A protective tube is provided for a temperature sensor. The
protective tube includes an inner metal tube including a chamber
for containing a temperature sensor, an intermediate refractory
sleeve surrounding and abutting at least a portion of the inner
metal tube, and an outer refractory sleeve cast onto the
intermediate refractory sleeve. The outer refractory sleeve covers
the intermediate refractory sleeve and the inner metal tube inside
the intermediate refractory sleeve. The intermediate refractory
sleeve is made of an elastic material such as a ceramic refractory
paper or coating or a fiberglass material that deforms during
expansion and contraction of the inner metal tube and the outer
refractory sleeve with changing temperature. The intermediate
refractory sleeve provides a buffer between the inner metal tube
and the outer refractory sleeve to minimize rupture of the outer
refractory sleeve which might otherwise occur during expansion and
contraction of the tube and sleeve with changing temperature.
Inventors: |
Wilson; Richard F. (Fort Wayne,
IN) |
Assignee: |
Pyromation, Inc. (Fort Wayne,
IN)
|
Family
ID: |
25081162 |
Appl.
No.: |
07/767,983 |
Filed: |
September 30, 1991 |
Current U.S.
Class: |
374/208; 136/230;
136/232; 136/234; 374/140; 374/E1.017 |
Current CPC
Class: |
G01K
1/125 (20130101) |
Current International
Class: |
G01K
1/08 (20060101); G01K 1/12 (20060101); G01K
001/12 () |
Field of
Search: |
;374/139,140,158,208,209
;136/230,232,233,234 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
2738926 |
|
Jun 1978 |
|
DE |
|
507835 |
|
Feb 1956 |
|
IT |
|
0956324 |
|
Apr 1964 |
|
GB |
|
Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Worth; W. Morris
Attorney, Agent or Firm: Barnes & Thornburg
Claims
What is claimed is:
1. A protective tube for a temperature sensor, the protective tube
comprising
means for containing a temperature sensor, the containing means
including a thermally conductive plug formed to include an inner
bore sized to receive a temperature sensor therein and an inner
metal tube formed to include an internal passageway sized to
receive temperature sensor lead wires therein and coupled to the
thermally conductive plug to cause the internal passageway to open
into the internal bore, the inner metal tube being made of a metal
having a first coefficient of thermal expansion,
outer refractory sleeve means for surrounding the thermally
conductive plug and at least a portion of the inner metal tube, the
outer refractory sleeve means being made of a ceramic refractory
material having a second coefficient of thermal expansion that is
different than the first coefficient of thermal expansion, and
buffer means for establishing a buffer between the outer refractory
sleeve means and the inner metal tube to separate the outer
refractory sleeve means and the inner metal tube and permit
expansion and contraction of the outer refractory sleeve means and
the inner metal tube with changing temperature so that each of the
inner metal tube and the outer refractory sleeve means can expand
and contract independently upon exposure to changing temperature
without rupturing the outer refractory sleeve means to accommodate
the differential thermal expansion rates of the inner metal tube
and the outer refractory sleeve means.
2. The protective tube of claim 1, wherein the inner metal tube is
a steel pipe.
3. The protective tube of claim 2, wherein the outer refractory
sleeve means is a ceramic tube having a first bore containing the
thermally conductive plug and a second bore containing the steel
pipe and the outer diameter of the steel pipe is less than the
inner diameter of the second bore to define a space between the
steel pipe and the ceramic tube.
4. The protective tube of claim 3, wherein the buffer means is a
deformable cushion located in the space to abut the steel pipe and
the ceramic tube and configured to yield during expansion and
contraction of the steel pipe and the ceramic tube to shield the
ceramic tube during exposure of the steel pipe and the ceramic tube
to a series of temperature change cycles.
5. The protective tube of claim 3, wherein the buffer means is an
elastic ceramic paper in the space between the steel pipe and the
ceramic tube.
6. The protective tube of claim 3, wherein the buffer means is an
elastic refractory material layer in the space between the steel
pipe and the ceramic tube.
7. The protective tube of claim 3, wherein the buffer means is a
preformed fiberglass sleeve in the space between the steel pipe and
the ceramic tube.
8. The protective tube of claim 1, wherein the buffer means
surrounds and abuts at least a portion of the inner metal tube and
the ceramic refractory material is cast onto the thermally
conductive plug and the buffer means to establish the outer
refractory sleeve and cover the thermally conductive plug and the
buffer means.
9. The protective tube of claim 8, wherein the buffer means is an
elastic ceramic paper wrapping surrounding the inner metal
tube.
10. The protective tube of claim 8, wherein the buffer means is an
elastic refractory material coating surrounding the inner metal
tube.
11. The protective tube of claim 8, wherein the buffer means is a
preformed fiberglass sleeve surrounding the inner metal tube.
12. The protective tube of claim 1, wherein the buffer means is a
deformable cushion abutting the inner metal tube and the refractory
sleeve means.
13. The protective tube of claim 12, wherein the deformable cushion
includes a first exterior surface abutting the inner metal tube, a
second exterior surface abutting the outer refractory sleeve means,
and an elastic core located between the first and second exterior
surfaces and configured to deform during expansion and contraction
of the inner metal tube and the outer refractory sleeve means.
14. The protective tube of claim 1, wherein the buffer means is an
elastic ceramic paper wrapping surrounding the inner metal
tube.
15. The protective tube of claim 1, wherein the buffer means is an
elastic refractory material coating surrounding the inner metal
tube.
16. The protective tube of claim 1, wherein the buffer means is a
fiberglass material surrounding the inner metal tube.
17. A protective tube for a temperature sensor, the protective tube
comprising
an inner metal tube,
a thermally conductive plug formed to include an inner bore sized
to receive the temperature sensor,
outer refractory sleeve means for surrounding the thermally
conductive plug and at least a portion of the inner metal tube the
outer refractory sleeve means being made of a ceramic refractory
material, and
buffer means for abutting each of the inner metal tube and the
outer refractory sleeve means and for permitting relative expansion
and contraction of the inner metal tube and the outer refractory
sleeve means with changing temperature so that the inner metal tube
and the outer refractory sleeve means can expand and contract
during exposure to a series of temperature change cycles without
rupturing the outer refractory sleeve means, wherein the buffer
means is an elastic ceramic paper wrapping surrounding the inner
metal tube means.
18. The protective tube of claim 17, wherein the inner metal tube
includes an exterior surface, the outer refractory sleeve means
includes an interior surface located in spaced relation to the
exterior surface of the inner metal tube to define an annular
buffer zone therebetween, and the buffer means is arranged to fill
the buffer zone to abut the exterior surface of the inner metal
tube and the interior surface of the outer refractory sleeve
means.
19. The protective tube of claim 17, wherein the inner metal tube
is a steel pipe.
20. The protective tube of claim 19, wherein the outer refractory
sleeve means is a ceramic tube having a bore containing the steel
pipe.
21. A protective tube for a temperature sensor, the protective tube
comprising
means for containing a temperature sensor, the containing means
including an inner hollow metal tube and a plug having an inner
bore with both the bore and tube hollow being sized to receive the
temperature sensor therein,
an outer refractory sleeve surrounding the plug and at least a
portion of the inner metal tube and forming an annular space
between the inner metal tube and the outer refractory sleeve,
the outer refractory sleeve being made of a ceramic refractory
material, and
an intermediate elastic buffer means lying in the annular space and
deforming during expansion and contraction of the inner metal tube
and the outer refractory sleeve with changing temperature.
22. A protective tube for a temperature sensor, the protective tube
comprising
means for containing a temperature sensor, the containing means
including an inner hollow metal tube and an attached plug with an
internal passageway therein,
an outer refractory sleeve surrounding the plug and at least a
portion of the inner metal tube and forming an annular space
between the inner metal tube and the outer refractory sleeve,
the outer refractory sleeve being made of a ceramic refractory
material, and
an intermediate elastic buffer means lying in the annular space and
deforming during expansion and contraction of the inner metal tube
and the outer refractory sleeve with changing temperature, the
buffer means being an elastic ceramic paper wrapping surrounding
and abutting the inner metal tube.
23. The protective tube of claim 22, wherein the outer refractory
sleeve is a ceramic refractory material cast onto the elastic
ceramic paper wrapping to enclose a portion of the inner metal tube
and intermediate elastic buffer means therein.
24. The protective tube of claim 21, wherein the outer refractory
sleeve is a ceramic refractory material cast onto the elastic
ceramic paper wrapping.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a protective tube for a temperature
sensor, such as a thermocouple assembly, which is used for
measuring temperatures of a material, such as a molten metal. More
particularly, this invention relates to a temperature sensor
protection tube having a metal tube for housing a temperature
sensor and a refractory material covering the metal tube.
It is often necessary to measure the temperature of molten metals,
such as aluminum and steel, during production or other industrial
processes. The temperatures encountered in these operations are
quite high, typically ranging from 660.degree. C. to 1,540.degree.
C. and higher. In addition, the corrosive nature of the
metallurgical processes involved present problems which must be
addressed in the design of protective apparatus for immersible
temperature sensors. Materials such as slag and molten metal
encountered in various metallurgical processes are corrosive and
abrasive and can dissolve and erode protective devices used to
cover and protect immersible temperature sensors.
It has been observed that protective tubes including a metal inner
tube having a hollow region containing a temperature sensor and a
refractory material casing surrounding the metal inner tube are
reliable in operation, and relatively simple and inexpensive to
manufacture. For example, U.S. Pat. No. 4,871,263 discloses a
protective tube which protects a temperature sensor from a hostile
molten metal environment and which allows the temperature sensor to
respond rapidly to temperature changes of the material whose
temperature is to be measured.
It has also been observed that the metal tube and ceramic
refractory material used to construct practical and effective
temperature sensor protection tubes expand and contract at
different rates with changing temperature. This is because the
metal in the inner tube and the ceramic refractory material in the
outer casing have different coefficients of thermal expansion.
Temperature variations cause dimensional changes in all materials.
Most materials tend to expand in size when heated and contract in
size when cooled. Within moderate ranges of temperature, the change
in length per unit length is practically constant and is called the
coefficient of thermal expansion.
Temperature sensor protection tubes are frequently exposed to rapid
temperature changes whenever these tubes are immersed into a hot
molten metal. The metal tube and ceramic refractory casing in the
protective tube are subjected to appreciable changes in
temperature. These elements expand and contract axially and
radially at different rates and develop internal stresses of
considerable magnitude during each cycle of temperature change.
An outer ceramic casing including in a temperature sensor
protection tube can rupture if it is not able to expand or contract
axially and radially somewhat relative to the other elements in the
protection tube as the elements in the tube expand and contract
with changing temperatures. For example, if the outer ceramic
casing is bonded or fitted to an inner metal tube, it is restrained
so as to prevent free thermal deformation. Large temperature
changes in a restrained outer ceramic casing can produce critical
internal stresses and even lead to rupture of the brittle
refractory material used to form the sleeve.
There exists a need for a protective device for a temperature
sensor which is able to withstand repeated rapid temperature
changes without rupturing the brittle outer ceramic refractory
casing. A protective device that is configured to permit an inner
metal tube and an outer ceramic casing to expand and contract at
different rates would be welcomed in the industry.
According to the present invention, a protective tube is provided
for a temperature sensor. The protective tube includes an inner
metal tube having a hollow region for containing a temperature
sensor, an outer refractory sleeve surrounding the inner metal tube
and forming an annular space therebetween, and an intermediate
elastic buffer member positioned in the annular space to lie
between the inner metal tube and the outer refractory sleeve. The
intermediate elastic buffer member is made of a cushion material
that deforms during expansion and contraction of the inner metal
tube and the outer refractory sleeve with changing temperature to
protect the brittle outer refractory sleeve from rupture.
In preferred embodiments, the inner metal tube is a steel pipe and
the outer refractory sleeve is a cast ceramic refractory casing.
The intermediate elastic buffer is either a ceramic paper wrapping,
a ceramic refractory coating, or a preformed fiberglass sleeve.
These buffers function to provide an elastic cushion between the
metal inner tube and the outer refractory sleeve which permits the
tube and sleeve to expand and contract at different rates during
immersion of the protective tube assembly to high temperature
molten metals and other materials. At the same time, the buffer
provides a base on the exterior of the metal inner tube that
permits the ceramic refractory sleeve to be cast in place without
establishing a bond to or tight fit with the inner metal tube.
Essentially, the ceramic refractory sleeve can be retained in place
in the protective tube assembly in such a way that it is free to
expand and contract at a rate different than the inner metal tube
during repeated rapid temperature cycles. Advantageously, the
improved protective tube assembly is configured to minimize ceramic
rupture problems often caused by expansion and contraction of and
internal stresses in elements used to construct the protective tube
assembly.
Additional objects, features, and advantages of the invention will
become apparent to those skilled in the art upon consideration of
the following detailed description of preferred embodiments
exemplifying the best mode of carrying out the invention as
presently perceived.
BRIEF DESCRIPTION OF THE DRAWINGS
The detailed description particularly refers to the accompanying
figures in which:
FIG. 1 is a partial cross-sectional side view of a protective tube
assembly according to certain preferred embodiments of the present
invention; and
FIG. 2 is a partial cross-sectional side view of a protective tube
assembly according to other preferred embodiments of the present
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
A first preferred embodiment of a protective tube assembly 10,
constructed in accordance with the present invention, for receiving
and protecting a temperature sensor such as a thermocouple
assembly, is shown in FIG. 1. A metal inner tube 12 has an open end
14 on an immersible end thereof, and an open end 16 on an opposite
non-immersible end. Metal inner tube 12 can be made of several
materials including, by way of example only, carbon steel,
stainless steel, or nickel alloy steel. A commercially available
tubing or pipe of standard dimensions can be used.
A thermally conductive plug 18 is mounted on the metal inner tube
12 so that an inner bore 20 formed in the thermally conducted plug
18 is arranged to contain a temperature sensor 22 therein. Thus,
inner bore 20 extends outwardly from the open end 14 of the metal
inner tube 12. As shown in FIG. 1, plug 18 can include internal
threads that mate with external threads on the open end 14 of metal
inner tube 12 to establish a threaded connection 29. Reference is
hereby made to U.S. Pat. No. 4,871,263 for a description of other
suitable plug-mounting techniques. During assembly, the temperature
sensor 22 and its wire leads 24, 26 are passed through the
passageway extending through the metal inner tube 12 and the open
mouth of open end 14 to reach the bore 20 formed in thermally
conductive plug 18.
Several different types of thermally conductive materials can be
used to construct plug 18. However, the use of graphite or silicon
carbide is preferred. Specific examples of such materials which may
be used are Union Carbide Corp. Type AGSR or AGSX graphite material
and products sold by Ferro Corporation, such as silicon nitride
bonded silicon carbide, KELLOGG 3AD silicate bonded silicon carbide
or recrystallized silicon carbide. Such a plug 18 will provide fast
thermal response to process temperature changes.
Much of the exposed exterior surface 32 of metal inner tube 12 that
extends outwardly from the inner bore 20 in thermally conductive
plug 18 is surrounded and covered with a thin buffer or cushion 34
as shown, for example, in FIG. 1. In the preferred embodiment
illustrated in FIG. 1, cushion 34 is a ceramic refractory paper 36
wrapped around the exposed exterior surface 32 of metal inner tube
12. As shown in FIG. 1, one edge 38 of paper 36 is wrapped to
overlap another edge 40 of paper 36 during installation of the
paper 36 on the metal inner tube 12. These edges 38 and 40 can
either be secured in place with fiberglass tape (not shown) or left
unbonded to one another to permit paper 36 to swell or move
somewhat to enhance the buffering or cushioning effects provided by
cushion 34. Several different types of ceramic refractory paper can
be used to provide a suitable elastic cushion means around metal
inner tube 12 and accommodate repeated expansion and contraction of
metal inner tube 12 with changing temperatures. For example,
FIBERFRAX -Ceramic Fiber Paper Nos. 970 and 550, available from
Carborundum Company, Refracturies Division, Sanborn, N.Y., provide
suitable elastic buffers. The cushion established by such a ceramic
refractory paper 36 is about 1/16" thick when wrapped about a metal
inner tube 12 having an outer diameter of about 0.500 inches.
In another embodiment (not shown), a ceramic rcfractory coating can
be used in lieu of ceramic refractory paper 36. For example, a thin
coating of THERMBRAKE 2X, available from Stellar Materials,
Detroit, Mich., could be used to provide a suitable buffer or
cushion around metal inner tube 12. Also, a preformed fiberglass
sleeve of the type shown in FIG. 2 could also be used. For example,
a fiberglass sleeve, available from Varflex Corporation, Rome,
N.Y., could be used in lieu of either the ceramic refractory paper
36 or coating (not shown).
In the preferred embodiment shown in FIG. 1, metal inner tube 12
has an outside diameter which is substantially constant over the
length of the tube 12. The outer diameter of the thermally
conductive plug 18 is larger than the outer diameter of the tube 12
and the plug 18 includes a stepped shoulder 42 adjacent to cushion
34.
An outer ceramic refractory sleeve 44 surrounds and envelopes the
metal inner tube 12 and the thermally conductive plug 18. As shown
in FIG. 1, only a very thin coating 46 of ceramic refractory
material in sleeve 44 covers the major portion of thermally
conductive plug 18 to enhance exposure of plug 18 to the
temperature of the material to be measured when the protective tube
10 is immersed.
According to certain preferred embodiments, the sleeve means 44 is
a refractory ceramic fiber material that is cast onto the plug 18
and the cushion 34 covering the metal inner tube 12 to provide the
ceramic refractory casing for the protective tube assembly 10.
Examples of suitable refractory ceramic fiber materials to form
sleeve 44 include THERMBOND 2800 85 refractory, available from
Steller Materials Incorporated of Detroit, Mich.; PLICAST AL-TUFF
85 EX, available from PLIBRICO of Chicago, Ill.; and ALUGARD 75 LW,
available from C-E Refractories of Valley Forge, Pa. A variety of
other commercially available ceramic refractory materials are
suitable.
As shown in FIG. 1, the cushion 34 occupies the annular space
provided between the exterior surface of the inner metal tube 12
and the interior surface of the cast ceramic refractory sleeve 44.
The cushion 34 is made of a resilient and elastic material that
deforms during expansion and contraction of the inner metal tube 12
and the outer refractory sleeve 44 with changing temperature. This
deformation allows the inner metal tube 12 to expand and contract
relative to the surrounding outer refractory sleeve 44 without
applying radially outwardly directed forces sufficient to rupture
the brittle refractory sleeve 44. Also, the sleeve 44 is not
restrained by the inner metal tube 12 or any adhesive bonds or
close fits from undergoing substantially free thermal deformation.
This freedom of the sleeve 44 to expand and contract during
exposure to repeated and rapid temperature changes help to minimize
the development of thermal loads or internal stresses in sleeve 44.
As noted above, large temperature changes in a restrained ceramic
refractory piece can produce critical internal stresses and even
cause rupture of the brittle refractory material used to form the
sleeve 44.
In other embodiments (not shown), other materials may be used to
provide a buffer between the inner metal tube 12 and the outer
refractory sleeve 44 to provide, in effect, a thermal expansion
joint between tube 12 and sleeve 44. For example, a crushable or
compressible material could be used as a buffer layer in lieu of an
elastic material. Such a crushable material would deform at least
during expansion of the tube 12 and sleeve 44 with hotter
temperatures but would not necessarily recover its original shape
fully during subsequent contraction of the tube 12 and sleeve 44
with cooler temperatures. This type of crushable buffer could
provide a suitable cushion layer between tube 12 and sleeve 44 in
applications where the temperature sensor is designed for only one
exposure or a few exposures to high temperatures.
Another embodiment of the invention is shown in FIG. 2. In this
embodiment, a disposable temperature sensor protection tube
assembly 50 is disclosed. This assembly 50 is intended primarily
for use in molten non-ferrous metals, specifically for molten
aluminum and zinc. Of course, a protection tube of this type could
be provided for protecting a wide variety of temperature sensors
and immersibles into many high temperature materials.
As shown in FIG. 2, the assembly 50 includes an inner metal tube 52
containing a temperature sensor 54 such as a thermocouple, an outer
refractory sleeve 56, and an intermediate layer of fiberglass
material 58 to provide a buffer between the inner metal tube 54 and
the outer refractory sleeve 56. In this embodiment, the immersible
end 59 of the inner metal tube 52 is welded closed as shown in FIG.
2 so that it is not necessary to close an open end of the inner
metal tube with a graphite plug of the type shown in the embodiment
of FIG. 1. Preferably, the inner metal tube 52 is a carbonized or
stainless steel and the outer refractory sleeve 56 is a cast
ceramic material.
A preformed fiberglass tube 58 provides an elastic buffer between
the inner metal tube 12 and the outer refractory casing 56. As
noted above, fiberglass tube, available from Varflex Corporation of
Rome, N.Y., are well suited for this purpose. Such a tube deforms
and recovers its shape during expansion and contraction of the
inner metal tube 52 and the outer refractory casing 56 to minimize
the possibility that casing 56 might rupture during exposure to
changing temperatures. A ceramic refractory material is cast in
place about the inner metal tube 52 and the intermediate fiberglass
buffer 58 to produce the outer ceramic casing 56.
Wire leads 60, 62 extend through the passage 64 formed in the inner
metal tube 52 from the temperature sensor 54 to a point outside of
the inner metal tube 52 as shown in FIG. 2. These wire leads 60, 62
are covered with insulation 66. A plug 68 of high temperature
ceramic cement is used to hold the wiring assembly 66 in place
inside inner metal tube 52. This plug 68 is used in lieu of
weldment and seals the inside of the tube 52 to protect the
thermocouple.
This assembly 50 provides good resistance to thermal shock,
mechanical breakage, and to penetration by molten aluminum and
zinc. Its small diameter also provides fast thermal response to
process temperature changes.
Although the invention has been described in detail with reference
to preferred embodiments and specific examples, variations and
modifications exist within the scope and spirit of the invention as
described and as defined in the following claims.
* * * * *